Is this going to be a 1 and done cook or a more regular thing? I've got a basic pull behind pig cooker that is made from a 275gal trailer that works great. So do the cinder block pits.
If a one time or rare use you might be able to rent one locally. Around me there are people who advertise rental of their pits, as well as the local ACE Hardware rents meadow creek cookers. Might want to call around locally and see if anyone has something you can rent.
If planning on doing this more often, renting a few different ones will allow you to try different style of cookers without having to invest a lot until you figure out what you want.
Another option would be a quick and easy Caja China or Cajun Microwave. Don't quite get the same smoke effect, but you can find them online for and they are pretty straight forward. Especially for a 1st time or 1 time use.